Inside Health

With Diseased Animals, Disposal Isn't Simple

By DENISE GRADY

Published: January 6, 2004

Whatever causes mad cow disease is practically indestructible. Even after being steamed, frozen, disinfected, zapped with ultraviolet light or bombarded with X-rays, tissue from sick animals can still spread the illness. Though scientists argue over whether the infectious agent is a bit of protein known as a prion or a mysterious viruslike particle, they agree it is devilishly hard to destroy.

And that gives rise to a queasy thought: given that animals and people can contract mad cow disease by ingesting infected tissue, is there a safe way to dispose of diseased carcasses?

The question may seem premature, since only one case of mad cow disease has been reported in the United States. But mad cow disease is one of several brain diseases known as spongiform encephalopathies, and there are hundreds of cases of other such diseases in this country: scrapie in sheep and chronic wasting disease in deer and elk.

Health officials have fretted about how to get rid of the dead animals. Carcasses have been rendered and incinerated, but those processes may not destroy prions. Rendered animal flesh added to feed is suspected of having started the mad cow epidemic in Britain.

Dr. Lisa Ferguson, a senior staff veterinarian at the Agriculture Department, said the department favored dissolving carcasses in tissue digestors, vats of lye that are essentially giant pressure cookers heated to 300 degrees Fahrenheit. The process, alkaline hydrolysis, has been patented by a privately held Indianapolis company, Waste Reduction by Waste Reduction Inc., or WR2. The company sells equipment that it says will destroy prions and liquefy a 1,500-pound cow in six to eight hours.

The process leaves behind only about 76 pounds of bone and teeth remnants that can be crumbled by hand into bone-meal powder, and 375 gallons of a sterile solution of water containing sugars, soaps and molecules that are the building blocks of proteins. Both the liquid and the powder can be used as fertilizer. The liquid, which the company described as "nonjelling" and "with a soaplike odor," can be safely dumped into a sanitary sewer, the company says. But large volumes of the liquid would need sewage treatment before being released, because the fertilizer content is high enough to cause ecological problems in waterways.

Joseph H. Wilson, company president, said that there is no smoke or fumes, because the tissue digestor is sealed, and that what comes out does not smell too bad.

"Compared to meat processing or rendering, our process is a breath of fresh air," Mr. Wilson said, adding that the ideal use for the liquid and the powdered remains would be as fuel in a biomass power plant.

The company, which began making tissue digestors for laboratories in 1993, makes vessels that can hold up to 10,000 pounds, enough to dissolve several carcasses at once. A digestor that size would cost about $1 million, Mr. Wilson said. Adding a building to house it, a water system and equipment to hoist dead animals would bring the total to $1.5 million to $2 million. The company's Web site displays a design for a plant that could process 240 tons of carcasses a day in the event of an epidemic.

Mr. Wilson said the company had proposed digestors that could hold 20,000 or 40,000 pounds to help the meat industry dispose of brain, spinal and intestinal tissues no longer allowed in the meat supply. He estimated that a large meatpacking operation could produce half a million pounds a day of such material.

About 30 to 40 digestors are in use in the United States, and at least 5 are on order for veterinary schools and animal diagnostic centers, Mr. Wilson said.

"We are growing rapidly," he said, noting that sales in 2003 were three to four times those of the year before. "We expect this coming year to triple again."

The reason for the growth has not been mad cow disease, Mr. Wilson said, but rather the increases in chronic wasting disease in deer and elk in the West and Midwest.

The Agriculture Department uses tissue digestors at its laboratories in Ames, Iowa, and Laramie, Wyo., and the veterinary college at Colorado State University in Fort Collins uses one to destroy the carcasses of deer and elk with chronic wasting disease, the company said. In Florida, the State Anatomical Board operates a digestor at Shands Hospital in Gainesville to dispose of cadavers used to teach anatomy.

The digestor in Ames, a 7,000-pound model, was trucked there on an emergency basis in 2001 to destroy more than 50,000 pounds of carcasses from a herd of sheep that the department had seized from a Vermont farm. The sheep, imported from Belgium, were destroyed because health officials suspected they had eaten feed contaminated with tissue carrying mad cow disease. The Ames digestor will be permanently installed sometime early this year, Mr. Wilson said.